Traffic control systems are ubiquitous in modern transportation systems. Traffic control systems are commonly used to regulate the flow of motorized vehicles, non-motorized vehicles and pedestrians on roads, streets, highways, bridges, and other surface transportation media designated for such purposes. Henceforth, the term “roadway” will be used to include any surface transportation media. Traffic control systems use visible indicators to direct when travel is permitted or not permitted on designated roadways. The purpose of traffic control systems is to provide safe and efficient access to the shared roadway for a specified group of roadway users. Crosswalks are portions of the roadway that are allocated for pedestrians to cross one or more roadways. They are identified by painted markings on the roadways and/or signage on the side of the roadway as described in the Manual for Uniform Traffic Controller Devices (MUTCD) which is available at http://mutcd.fhwa.dot.gov/htm/2003r1r2/html_index.htm.
A traffic control system is comprised of an electronic device that determines which vehicle and pedestrian signals are to be active to control movements through a designated portion of the roadway. As used herein, an intersection refers to the intersection of two or more roadways that share a common right of way in such a manner that one or more traffic movements must be constrained to avoid conflicts that may result in collisions. A signalized intersection is an intersection that uses a traffic control system to control vehicle and pedestrian movements at an intersection or on a roadway. The traffic control system may incorporate sensors that detect the presence of vehicles at specific places in the roadway. The traffic control system may also have detectors to sense when pedestrians press a button that signifies that they are requesting (calling for) service to be able to cross a specific element of the roadway.
Conventional traffic control systems used today consist of three essential elements: 1) the traffic controller that is responsible for determining which signals are on at any given time and, in some cases, processes sensor inputs, 2) one or more load switches that converts the traffic controller logic outputs to turn on and off 120 VAC, and 3) a conflict monitor (CM) or malfunction management unit (MMU) that monitors the outputs from the load switches to ensure safe operation by detecting signals that create a conflicts in traffic movements involving vehicles and, in some cases, pedestrians. The CM or MMU places the system into a safe fail mode if a conflict is detected.
Many traffic control systems provide control of pedestrian movements using visible and audible messages and/or symbols. According to the MUTCD, visible signals used to control pedestrian movements include illuminated signals that display the words “WALK”, “DON'T WALK”, and “WAIT.” Other traffic control systems use the illuminated symbol of a walking person in lieu of a “WALK” signal and a symbol of a hand in lieu of the “DON'T WALK” or “WAIT” signals. Some traffic control systems also include countdown timers that display the number of seconds remaining before the pedestrian is to be clear of the segment of the roadway shared with other users. In addition to the visible displays, some traffic control systems also broadcast audible messages in the form of verbal phrases or easily differentiable tones such as chirps and cuckoos that mimic bird calls.
Pedestrian movements at signalized intersections are controlled by displaying the “WALK” indication indicating that individuals should proceed to cross the designated roadway with due caution. The “WALK” display changes to a flashing “DON'T WALK” indicating that a pedestrian who is not already in the roadway should no longer leave the curb and enter the roadway. A non-flashing “DON'T WALK” display indicates to the pedestrian it is no longer safe to be in the roadway for the designated crossing.
Some pedestrian movements are controlled by the traffic controller that automatically allocates a regular fixed time interval for pedestrian crossings and requires no action by the pedestrian to register a request for service with the traffic controller. Some traffic control systems provide a sequence of displays to both vehicles and pedestrians when triggered by manual push buttons, or other pedestrian friendly features.
A pedestrian call system provides the means for pedestrian to request the traffic controller to provide a WALK indication during the appropriate interval associated with parallel traffic movement or provide an exclusive pedestrian movement. In the case of pedestrian movements combined with parallel vehicle movements, the timing of the vehicle movement may be extended to allow sufficient time for pedestrians to complete the crossing.
Usually the push buttons that are used by the pedestrian to register a request for service with the traffic controller are physically positioned in the proximity of the side of the roadway adjacent to the media used by motorized vehicles. The MUTCD gives guidelines as to the placement and orientation of the pedestrian activation buttons. However, variations of roadway geometries preclude consistent and predictable placement of the pedestrian call buttons at many signalized intersections.
The operation of today's traffic control systems provide a reasonable degree of safety provided that pedestrians and vehicle operators use their sight to identify potential hazards and conflicts as well as to correctly identify the signal lights that are illuminated to control their movements. Pedestrians with cognitive and visual acuity impairments must rely on auditory cues to assist them in lieu of visual signals. The difficulties of crossing a roadway for people with cognitive and vision impairments are described in detail in Harkey et al., “Accessible Pedestrian Signals: A Guide to Best Practices” (hereinafter “Harkey”) available at http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_w117a.pdf. Harkey's Appendix D (also available at http://www.walkinginfo.org/aps/appendix_d_understanding.cfm) discusses the safety and access difficulties faced by blind pedestrians. Both of these are incorporated herein by reference.
Unfortunately, although the proper operation of traffic signals is essential for safe passage of the visually impaired, pressing a call button merely activates a sequence of intended operations, but no confirmation of appropriate operation is available to the caller. Hence, visually impaired pedestrians rely on proper operation of traffic signaling systems, and cannot readily detect malfunctions. Accordingly, improved traffic control devices and methods are needed that permit visually impaired pedestrians to verify proper operation.